- A number of factors came together to spark what are arguably the costliest fires in state history.
- The drought worsened considerably in eastern Colorado starting in the summer.
- While high wind events are typical, the high winds on December 30 were exceptional.
Thursday’s Colorado wildfires were started and fanned by high winds, but their destructive seeds have been sown by months of drought and exceptionally hot, and climate change is lengthening the fire season in the west.
The rapidly spreading Marshall and Middle Fork fires burned more than 500 homes and forced more than 30,000 residents of southern Boulder and Broomfield counties to evacuate quickly on Thursday.
Devastating wildfires are what you’d expect to read in the summer, or if it’s California, in the fall.
But the fires, likely to become the costliest and most destructive in Colorado history, occurred just two days before New Year’s Day.
How is that possible in a state known for cold and snow at this time of year?
(FOLLOWING: Fire updates | How you can help victims)
From soaking to extreme drought
In late spring, the Front Range and eastern plains of Colorado were one of the few drought-free areas in the west, according to the June 1 Drought Monitor analysis. Colorado’s western slope experienced exceptionally drought, but the eastern half of Colorado experienced one of its wettest May on record, according to NOAA.
But then the faucet closed.
The second half of 2021, July through December 29, was Denver’s driest period in 150 years. Only 1.08 inches of precipitation fell in the town of Mile High during this roughly six month period, just 15% of average.
Denver had its first snowless fall. The first measurable snow did not fall on the city until December. It was a paltry three tenths of an inch that melted quickly.
Colorado sweated through a hot summer, then the state’s second hottest fall, then one of its hottest December months on record.
It’s no wonder the eastern half of the state went from a drought-free spell in late July to severe to extreme drought in December.
The lingering heat and lack of rain or snow left soil moisture among the lowest on record for late December, according to NOAA.
The Front Range was a powder keg. All that was missing was a spark.
This spark was provided by strong winds.
Strong winds are common along the Rocky Mountain Front Range from Montana to Wyoming, Colorado and New Mexico. But what happened on Thursday was far from typical.
“We are in the midst of a truly historic windstorm across the Front Range, the Foothills and the Urban Corridor.” (National Weather Service – Boulder, Colorado, in a discussion of the December 30 forecast)
With the jet stream directly over the Colorado, strong winds swept over the mountains. Since the air just above the mountain peaks was stable, strong winds were forced down the slopes of the Rockies to the Front Range.
According to the National Weather Service, numerous gusts of 80 to 100 mph have been recorded along the Front Range, including a gust to 115 mph in the western suburbs of Denver in Arvada, Jefferson County.
High winds knocked down power lines that are believed to have started the fires.
The fires spread rapidly through the dry vegetation.
And unlike a more typical Colorado wildfire in the highlands, the fires burned through the densely populated Front Range, rather than the forest.
Western fire season stretches
Climate change is extending the fire season.
The average fire season in the West lasts more than 100 days, burns six times as much land and triples the number of large fires today compared to the 1970s, according to Climate Central.
Indeed, the underlying conditions favorable to forest fires extend over much of the year. In the west, the snowpack is expected to arrive later in the fall, melt earlier in the spring, and generally decrease as temperatures increase.
Essentially, winter forest fires are on the rise.
On December 1, a forest fire broke out on the outskirts of Great Falls, MT, charring structures and forcing evacuations in part of the country where highs in the 1930s and lows among teenagers are more typical early December.
Two weeks later, the same storm system responsible for a historic Midwestern derecho and tornado outbreak caused rapid wildfires in Kansas and the Oklahoma and Texas Panhandles. The smoke from these fires was carried hundreds of kilometers into the Great Lakes.
In response, the US Forest Service is moving from the concept of a fire season to a fire year.
If you live in a drought-ridden area and your forecast calls for high winds, you need to consider the potential for a fast-spreading forest fire that could require you to evacuate quickly, no matter what the schedule says.
The main journalistic mission of The Weather Company is to report on the latest weather news, the environment and the importance of science in our lives. This story does not necessarily represent the position of our parent company, IBM.